An apprentice prepares a pair of tortoiseshell frames, looking at the turtle-shell's shades at Maison Bonnet's Sens workshop, south of Paris.

Joel Saget / AFP - Getty Images

A pair of tortoiseshell frames and its fact sheet containing the information of the future owner is found in Maison Bonnet's Paris workshop.

Joel Saget / AFP - Getty Images

Christian Bonnet and his apprentice Daniel work on pairs of tortoiseshell frames in the Maison Bonnet's Sens workshop.

Joel Saget / AFP - Getty Images

A Maison Bonnet workshop employee works on a pair of tortoiseshell frames.

Joel Saget / AFP - Getty Images

Franck Bonnet, adjusts a pair of spectacles on a customer in Maison Bonnet's Paris shop.

Joel Saget / AFP - Getty Images

A pair of $39,000 tortoiseshell spectacles, called pure blond, made by Christian Bonnet in Maison Bonnet's Paris workshop.

Four decades after the trade in tortoiseshell was banned under the 1973 CITES convention, the fourth-generation family firm, Maison Bonnet, sees itself as custodian of a rare craft, fashioning made-to-measure spectacles from stocks amassed before the ban.

Frames made by these artisans isn't an easy or an inexpensive process. Depending on the material, frames from Maison Bonnet can cost hundreds to tens of thousands of dollars and require a series of interviews and fittings.

The purchase of each pair of glasses is the result of a three-month operation, involving 20 hours of hand labor, and a process that includes 10 stages, 12 fittings, interviews, personality assessments and face measurements. Continuing reading NYTimes.com article.

Photos in this blog post were shot by AFP's Joel Saget in November, but made available to NBC News today.